Process of inhibiting the discoloration of photographic color images



PROCESS OF INHIBITIN G THE DISCOLORATION OF PHOTOGRAPHIC COLOR IMAGES HubertO. Ranger, South Hadley Falls, Mass., assignor to General Aniline & Film Corporation, New York, N. Y., a corporation of Delaware N Drawing. Application April 14, 1954, Serial No. 423,221

20 Claims. (Cl. 96-56) This invention relates to the treatment of color photographs and especially to final rinse baths for inhibiting the discoloration of color photographic materials in which color images have been formed by development with a primary amino developing agent.

Various treatments have been proposed to prevent the dye fading of color images formed by color forming development, but these treatments are largely ineffective in preventing the discoloration of the white areas when exposed to heat, high humidity, sunlight or ultraviolet light. In spite of the ordinary precautions which are taken in storing photographs, the whites will turn yellow when the color pictures are kept near windows, in billfolds or even in storage cabinets where they are subjected to heat or high humidity. This yellowing which affects not only the whites but also the pastel shades be comes even more pronounced when the color pictures are exposed to direct sunlight or to the limited amount of ultraviolet light which is given oif by fluorescent lamps. Prints processed without the use of color forming developmentdo not exhibit this stain.

The yellowing of the white image areas is most frequently observed in color photographs which are prepared by the use of color materials which contain color formers capable of forming, upon color development with a primary amino developing agent, azomethine and indoaniline (quinonimine) dyes. This lack of stability which leads to yellowing of the color pictures is highly undesirable because valuable color records are rendered useless after limited periods of storage.

It is an object of my invention to provide a method of treating colored photographs so that extreme conditions of humidity and heat and exposure to sunlight and ultraviolet light will not cause discoloration of the white areas.

Other objects and advantages will appear herein after.

I have found that the above objects are accomplished by employing, as a final rinse bath, an aqueous solution containing a stain inhibiting amount of a water soluble zinc salt. The following are examples of suitable zinc salts. p

Zinc acetate Zinc bromide Zinc chloride Zinc nitrate Zinc sulfate or ultraviolet light. This protection is achieved without' afiecting the original color balance. The concentration of the water soluble zinc..salt;em-

55 form a quinonnnme, indoanlhne or azomethtne dye withnitd States PatentO "ice 2 ployed may range from 0.5% to 15% by weight. Higher amounts give little improvement and prove, therefore, uneconomical. Concentrations on the order of from 2 to 5% give the best results. The rinsing time may be varied from a few seconds to several minutes, the optimum time being between 3 and 5 minutes.

The zinc salt solutions are employed in a slightly acidic medium corresponding to a pH range of from 3.5 to 6.5. A pH lower than 3.5 will affect adversely the color de veloped azomethine, indoaniline and quinonimine dyes, while a pH higher than 6.5 will cause the formation of zinc hydroxide fiocculates which may cling to the finished picture in the form of a scum. Solutions having a pH between the range of from 4.5 to 6.0 are preferred because they avoid the conditions of the pH ranges in which these undesirable side effects may take place. The desired range can be established by the addition of soluble acids such as acetic acid, alkalis such as sodium hydroxide, salts such as sodium acetate or buifering mixtures which do not form Water insoluble zinc salts.

A surface active agent may be added to improve the draining of the rinse and thus accelerate indirectly, the drying. Any commercially available anionic, cationic or non-ionic surface active agent may be employed so long as it is substantially colorless, possesses the desired wetting properties and is compatible with the water soluble zinc salt.

The exact mode of operation by which the zinc salts inhibit the yellowing of the white and pastel areas of the processed color pictures is still unknown. It is believed that the Zinc salt combines with the residual color formers to prevent the formation of quinoid decomposition or oxidation products. However, it is to be understood that this theoretical explanation should not be taken as an exact description of the role played by the zinc salts in preserving the color pictures.

The photographic multicolor materials in which the dyestufi images are produced with color formers present in the emulsion and which may be processed with the antistain bath of the present invention are color reversible film, color negative film, color reversible white printing material coated on an opaque base, and color positive printing material coated on paper.

The color reversible film consists of an integral tripack emulsion coated on the usual clear cellulose acetate, mixed cellulose ester or cellulose nitrate film base. Each of the emulsions is sensitized to one of the primary colors of light, namely, blue, green, and red. The top layer is blue sensitive. A filter layer, yellow in color and blue. absorbing, lies under the top layer. Below this filter layer,

I lies a green sensitive emulsion layer, and below this is a red sensitive emulsion layer. Each of the three silver halide emulsion layers contains dye forming compounds fast to diffusion which unite during the development of a silver image in an aromatic amino developing agent to the oxidation product of the developing agent. In most instances, the developed dye image is complementary in color to the color for which the emulsion layer is sensitized. Thus, a yellow dye is formed in the blue sensitive emulsion; a magenta. dye is formed in the green sensitive emulsion; and a cyan dye is formed in the red sensitive emulsion. Combinations of these three printing primaries will produce all of the other colors in the fin ishedfilm or print.

The silver which is formed during development must be removed after color development. This is done by the use of a bleach such as acidified alkali permanganate or alkali dichromatesolutions which convert the metallic silver into a water soluble silver salt or, by other bleach solutions which convert the metallic silver into a silver salt which is soluble in fixed solutions, particularly sod-ium thiosulfate solutions. Suitable bleach solutions of the second type include those which contain a halide and an oxidizing substance such as an alkali ferricyanide, a cupric salt or an alkali dichromate.

The color negative film is made up in the same manner as the color reversible film with the exception that it may contain an anti-abrasion layer of clear gelatin over the blue sensitive top layer. The color reversible white opaque material is prepared in the same manner as the color reversible film and the color negative film with the exception that the base consists of an opaque white film and that it may contain a layer of clear gelatin between the red sensitive layer and the green sensitive layer. The positive color paper is also constructed in the same manner as the color reversible film and the color negative film with the exception that the emulsion is coated on a baryta. coated paper base. Other differences between the negative, positive and reversal materials are based on the relative speed and contrast of the individual emulsion layers and of the multilayer color materials. Suitable methods for the preparation of photographic multilayer materials containing color formers fast to diffusion have been described in the literature relating to color photography and are, therefore, not described here.

The foil vving examples describe in detail the methods for $303051 lit-hing the above objects, but it is to be understood that they are inserted merely for the purpose of illustration and are not to be construed as limiting the scope of the invention. All parts and percentages are by weight unless otherwise stated.

Example I A 35 color transparency was printed by projection onto two 3" X sheets of color reversible white opaque film. The two exposed color reversible white opaque film sheets were first developed for 12 minutes at 68 F. in a developer of the following composition:

Water to make 1 liter.

The developed films were shortstopped for 3 minutes at 68 F. in a 5% aqueous solution of sodium bisulfate.

The films were washed for 2 minutes in running water at 68 F. and re-exposed to white light.

The re-exposed films were color developed for minutes at 68 F. in a developer of the following composition:

Gms. 4-aminodiethylaniline monohydrochloride 4 Sodium sulfite 2 Hydroxylamine hydrochloride 2 Sodium carbonate 80 Potassium bromide 2 Water to make 1 liter.

The color developed films were rinsed for 4 minutes in running water at 68 F. and hardened for 5 minutes in a 3% aqueous solution of potassium chrome alum.

The hardened films were washed for 5 minutes in running water at 68 F. The washed materials were then treated with a bleach bath of the following composition:

Dipotassium monosodium ferricyanide gms 100 Potassium bromide gms 15 Disodium phosphate gms 40 Sodium bisulfate gms Formalin (40%) cm.. 20

Water to make 1 liter.

The bleached films were washed for 5 minutes at 68 F. and then fixed for 5 minutes in a solution of the following composition:

Gms. Hypo 200 Water to make 1 liter.

After fixing, the materials were washed for 10 minutes in running water at 68 F.

After the final Washing, one print was allowed to dry while the other was rinsed for 4- minutes in a 3% aqueous solution of zinc chloride which was buffered to a pH of 5.5. The treated print was dried and then exposed together with the untreated print to direct sunlight at room temperature. After 5 days, the treated film did not show any noticeable yellowing in the white areas nor any discoloration in the pastel colored areas, whereas the un treated sample was badly yellowed in the white and'discolored in the pastel colored picture areas.

Example 11 A color negative was printed onto two sheets of positive color paper. The two exposed papers were developed for 15 minutes at 68 F. in a developer having the following composition:

Gms.

4 (di ,6 hydroxyethylamino)aniline monohydrochloride 5 Sodium sulfite 3 Sodium carbonate 60 Potassium bromide 2 Water to make 1 liter.

The color developed papers were rinsed for 10 minutes in running water at 68 F. and hardened for 5 minutes in a 3% aqueous solution of potassium chrome alum.

The hardened papers were washed for 5 minutes in running water at 68 F. and then treated with a bleach solution having the following composition:

Potassium bromide gms 20 Potassium dichromate gms 5 Potassium alum gms 40 lhosphoric acid (85%) Water to make 1 liter.

The pH of this bleach solution was adjusted to 3.5 by the addition of a small amount of sodium hydroxide. The bleached papers were washed, fixed and washed as described in Example I.

After the final washing, one of the prints was dried while the other print was dipped for 3 minutes in a 4% aqueous solution of zinc sulfate which had a pH of 5.0; briefly blotted and dried. r

The treated and the untreated prints were placed in a high humidity oven having a temperature of 50 C.

and a relative humidity of percent. After 5 days, the

prints were removed from the oven. The print which had received a final rinse in the zinc sulfate solution did not show any yellowing of the white areas while the untreated print was badly yellowed.

Example IV Example 'III was repeated with the exception that the dichromate bleach was replaced by a bleach solution having the following composition:

Water to make 1 liter.

avsaam The treated and the untreated prints were exposed to intense ultraviolet and visible light in a fadeometer for a period of 4 hours. An inspection of the exposed prints showed that the white and the pastel shaded areas of the treated print had retained their original brilliance while the corresponding areas of the comparison print were badly stained.

Example V Example I was repeated with the exception that the exposure to direct sunlight was replaced by a storage test in which the prints were kept in a room with northern exposure for a period of six months. The white and pastel colored areas of the color print which had been rinsed with zinc chloride retained their original pleasant appearance, whereas the untreated print badly dircolored, particularly in the white and light colored areas.

The above specific examples are to be regarded as being merely illustrative of the invention and not, in any sense, restrictive.

Various modifications such as substituting equivalent materials and varying the proportions of materials used will be obvious to persons skilled in the art. Therefore, the scope of the invention is to be limited solely by the appended claims.

I claim:

1. in the process of producing color photographic images in a photographic material comprising a support and at least one light sensitive silver halide emulsion layer containing a color former fast to diffusion capable of forming dye images with the oxidation products of a primary amino developing agent by exposing said material, color developing, bleaching, fixing and washing the same, the improvement which comprises avoiding the formation of stain by treating said material after the final washing operation with an aqueous solution containing, in an antistaining amount, a Water soluble Zinc salt.

2. In the process of producing color photographic images in a photographic material comprising a support and at least one light sensitive silver halide emulsion layer containing a color former fast to diffusion capable of forming, upon development with a primary amino developer, dye images selected from the class consisting of azomethine and indoaniline dyes by exposing said material, color developing, bleaching, fixing and wash ing the same, the improvement which comprises avoiding the formation of stain by rinsing the said material after the final washing operation with an aqueous solution containing, in an antistaining amount, a water soluble zinc salt.

3. In the process of producing colored photographic images in a photographic material comprising a support and at least one light sensitive silver halide emulsion layer containing a color former fast to diffusion capable of forming, upon color development with a primary amino developing agent, dyes selected from the class consisting of azomethine and indoaniline dyes, said process including exposing the film, color developing, bleaching, fixing and washing the same, the improvement which comprises avoiding the formation of yellow stain in the white areas by rinsing said color material after the final washing operation with an aqueous solution containing, in an antistaining amount, a water soluble zinc salt, said solution having a pH between the range of 4.5 and 6.0.

4. A process according to claim 1 wherein the anti staining amount of said water soluble zinc salt is on the order of from 9.5 to 15 grams.

5. A process according to claim 1 wherein said water ble Zinc salt is Zinc chloride.

6. A process according to claim 1 wherein said water soluble zinc salt is zinc sulfate.

7. A process according to claim 1 wherein said water soluble zinc salt is zinc acetate.

8. A process according to claim 2 wherein the antistaining amount of said water soluble Zinc salt is on the order of from 2 to 5 grams.

9. A process according to claim 2 wherein said water soluble zinc salt is zinc chloride.

1.0. A process according to claim 2 wherein said water soluble zinc salt is zinc sulfate.

11. A process according to claim 2 wherein said water soluble zinc salt is zinc acetate.

12. A process according to claim 3 wherein said water soluble zinc salt is zinc chloride.

13. A process according to claim 3 wherein said water soluble zinc salt is zinc sulfate.

14. A process according to claim 3 wherein said water soluble zinc salt is zinc acetate.

15. A process according to claim 1 wherein said support is paper.

16. A process according to claim 1 wherein said support is a white opaque film.

17. A process according to claim 2 wherein said support is paper.

18. A process according to claim 2 wherein said support is a white opaque film.

19. A process according to claim 3 wherein said support is paper.

20. A process according to claim 3 wherein said support is a white opaque film.

References Cited in the file of this patent UNITED STATES PATENTS 2,515,121 Harsh July 11, 1950 2,518,686 Harsh Aug. 15, 1950 2,706,687 Rees et a1. Apr. 19, 1955 

1. IN THE PROCESS OF PRODUCING COLOR PHOTOGRAPHIC IMAGES IN A PHOTOGRAPHIC MATERIAL COMPRISING A SUPPORT AND AT LEAST ONE LIGHT SENSITIVE SILVER HALIDE EMULSION LAYER CONTAINING A COLOR FORMER FAST TO DIFFUSION CAPABLE OF FORMING DYE IMAGES WITH THE OXIDATION PRODUCTS OF A PRIMARY AMINO DEVELIPING AGENT BY EXPOSING SAID MATERIAL, COLOR DEVELOPING, BLEACHING, FIXING AND WASHING THE SAME, THE IMPROVEMENT WHICH COMPRISES AVOIDING THE FORMATION OF STAIN BY TREATING SAID MATERIAL AFTER THE FINAL WASHING OPERATION WITH AN AQUEOUS SOLUTION CONTAINING, IN AN ANTISTAINING AMOUNT, A WATER SOLUBLE ZINC SALT. 